In spinal deformity surgical procedures, the curvature of the spine (e.g., the coronal curvature of the spine and/or the sagittal curvature of the spine) can be corrected by the implantation of a construct of bone anchors and spinal fixation elements. Examples of bone anchors used in such a construct include hooks and bone screws. Examples of spinal fixation elements used in such a construct include rods and tethers.
During spinal deformity surgical procedures, a surgeon typically first exposes the spine posterior and attaches bone anchors to selected vertebrae of the spine. The surgeon then inserts a spinal fixation element into receiving portions of the bone anchors to connect the selected vertebrae, thereby fixing the relative positions of the vertebrae.
In addition to correcting the curvature of the spine, the angular rotation of one or more vertebrae relative to other vertebrae around the axial plane of the vertebra may also be corrected. Conventional surgical procedures for correcting the angular relationship of a vertebra involve rotating the spinal fixation element, for example, a spinal rod, connected to the vertebra by a bone anchor. In the case of constructs that include a spinal rod, this procedure is typically referred to as “derotation.” Derotation can place significant stress on the interface between the bone anchors connected to the rotated spinal rod and the vertebra in which each bone anchor is implanted. This stress can cause a failure of one or more of the bone anchors or harm to the vertebra. Accordingly, there is a need for improved instruments and methods for manipulating a vertebra.
Conventional derotation instruments are designed to be used after reduction has been performed and the spinal fixation element has been secured to the bone anchor. However, the bone anchors often bind on the fixation element during the rotation, preventing the motion or requiring significant force to obtain it. Thus in some instances it may be beneficial to perform derotation before insertion of the spinal fixation element. Being able to insert the rod after derotation reduces the need for significant reduction, complicated rod contouring and in-situ bending thereby decreasing the complexity of the procedure.